<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Canvas</title>
  <style>
    .container {
      margin: 100px auto 0;
      width: 400px;
      height: 400px;
    }
    #round1 {
      width: 400px;
      height: 400px;
    }
  </style>
</head>
<body>
  <div class="container">
    <canvas id="round1"></canvas>
  </div>
</body>
<script>
  var elmRound = document.querySelector('#round1');
  var cxt = elmRound.getContext('2d');
  cxt.beginPath();
  cxt.lineCap = 'round';
  cxt.lineWidth = '4';
  cxt.strokeStyle = '#fff';
  cxt.arc(75, 75, 20, 0, 2*Math.PI-(Math.PI/2), false);
  cxt.stroke();
</script>
</html>